This invention relates to fixtures and devices for holding a blade of a tool such as a chisel or plane iron, for purposes for grinding or honing the blade.
A tool having a blade must be sharpened from time to time in order for it to work properly and efficiently. A wide variety of tools with blades that require sharpening are known and these include chisels used in woodworking and plane irons used in planning tools. The width of the blade to be sharpened can vary between less than one half inch to two to three inches or more. Generally, the sharpening operation can include the basic steps of grinding a basic bevel angle on the edge of the blade using a grinding wheel. Then, in order to obtain a particularly sharp edge on the blade, a honing stone is used to hone a microbevel at a slightly different angle than the basic bevel angle which has been ground. Since the secondary bevel is small, the person sharpening the tool will remove less steel and arrive at a sharp edge quickly. However, in the past, it has generally required considerable skill for a person to sharpen such tools with a microbevel without causing any damage to the blade. This is particularly true for a longer blade edge of two, three or more inches since it can be difficult to hold the blade at the correct orientation both for the grinding step and the honing step.
One known sharpening system marketed by Lee Valley Tools Ltd., of Ottawa, Ontario, Canada, is a honing guide and angle jig set sold under the registered trade-mark VERITAS. This known apparatus includes a flat metal support plate on which a five-sided angle setting wheel is bolted near one end of the plate. Each side or facet of the wheel provides a different selected angle for the blade to be sharpened. The blade is mounted in a clamping device which has an opening to receive a central portion of the blade and a clamping bolt that engages the side of the blade. Mounted on the bottom of the clamping device is a wide roller which is arranged on an adjustable cam shaft. With this rolling jig, the blade to be sharpened can be rolled back and forth along a honing stone at the correct angle to form the desired micro-bevel. Although this known jig set may be satisfactory for forming the micro-bevel on the blade, it is not well suited for creating or grinding the basic bevel angle for the tool prior to the honing operation.
There has also been developed by the applicant an apparatus which can be used for both grinding and honing the blade of a tool, this apparatus being described in more detail hereinafter and illustrated in the FIGS. 1 to 5. This prior art apparatus includes a clamping mechanism for holding the blade, which is mounted on a pivotal elongate arm extending in a first plane. The arm is mounted on a tubular support member which has a passage formed therein. The central axis of this passage defines a pivot axis perpendicular to the first plane. This known apparatus includes a mounting bar device with an elongate mounting bar on which the tubular support member can be mounted for a grinding operation. The mounting bar device includes an adjustable base or support mountable on a workbench. During a grinding operation with a grinding wheel, the adjustable support rigidly holds the mounting bar so that the bar and the tubular support member extend parallel to the axis of rotation of the grinding wheel. The support member can be moved along die bar and rotated on the bar during grinding.
Although the above described grinding and honing apparatus works satisfactory for its intended purpose and can be used for both grinding and honing, there are some aspects of the apparatus which can cause difficulty for some users. For example, the clamping mechanism of this known apparatus can make it difficult to sharpen a short tool or blade. In addition there is no provision in this apparatus for self squaring of the tool or blade in the clamping mechanism, thus necessitating extra care to ensure that the tool or blade is properly oriented in the clamping mechanism. Furthermore, it can be difficult to set the blade in the clamping mechanism so that it extends parallel to the grinding surface of the grinding wheel as desired without having to make careful, time consuming adjustments to the position of the blade in the clamping mechanism or without manufacturing the apparatus to very precise tolerances.
There is provided and described herein an improved blade holding jig for grinding a blade with a grinding machine, this jig employing a clamp unit with a U-bracket having two spaced-apart legs and two clamping jaws adjustably mounted on the U-bracket between the legs. The clamping jaws can be moved towards one another to firmly clamp the blade or moved away from one another to release the blade.
Also a main part of the blade holding jig described herein can be used for honing a blade to provide a sharp edge. In an exemplary version of this blade holding jig used for honing, an attachment mechanism adjustably connects one of the legs of the U-bracket to an end section of the arm member which is opposite the end on which the tubular support member of the support arm mechanism is mounted. Using this jig for honing, the clamp unit and the blade clamped therein can be set at a desired angle for the honing operation by using the attachment mechanism.